1. Field of the Invention
The present invention relates to a wafer processing method of grinding a rear surface of a wafer and dividing the wafer into individual devices.
2. Description of the Related Art
A wafer formed with a plurality of devices such as ICs is ground from the rear surface to have a given thickness and then divided by a dicing device or the like into individual devices, which are used in various electronic devices. In recent years, to make it possible to reduce the weight and size of electronic devices, a wafer has been formed by grinding to be as extremely thin as 100 to 20 μm. However, the wafer is formed thin to become soft, which poses problems for subsequent conveyance and of making it difficult to cover a ground surface with a metal film such as gold, silver, titanium or the like with a thickness of several tens nm for electrically testing devices.
To eliminate such problems, the following wafer processing method has been proposed and a patent application has been made by the present applicant (e.g. Japanese Patent Laid-open No. 2007-19379). In this method, a protection tape is stuck to the front surface of the wafer, and only a portion, of the rear surface of the wafer, corresponding to the rear side of the device area is ground to form a thick ringlike reinforcing portion on the outer circumferential side thereof. This can facilitate the conveyance of the wafer and make it easy to perform the subsequent metal film forming step. In the invention described in Japanese Patent Laid-open No. 2007-19379, the metal film is coated on the rear side of the device area with the ringlike reinforcing portion having been formed. Thereafter, the rear surface of the ringlike reinforcing portion is ground to make the rear surface of the wafer flat. Alternatively, after the ringlike reinforcing portion is cut and removed, the protection tape is peeled from the front surface of the wafer and a dicing tape is stuck to the rear surface for dicing, whereby the wafer is divided into individual devices.